JP5140301B2 - Phase difference detector and phase difference detection method - Google Patents

Description

  The present invention relates to a phase difference detector and a phase difference detection method for measuring an interference distance in which a distance and a displacement amount are measured using optical interference.

  Laser interferometers are widely used to measure distance or displacement. As such an interferometer, there is a polarization interferometer that emits a coherent light beam to a polarization beam splitter and generates two orthogonal polarization beams by the polarization beam splitter. Of these two orthogonally polarized light beams, one polarized light beam is emitted along a reference optical path having a fixed length of the interferometer, and the other polarized light beam is emitted along a distance measuring object optical path, that is, a measured object optical path. Is done. Each of the two polarized light beams passes through the quarter-wave plate and is reflected by the reference surface and the object surface. The reflected polarized light is returned back through the quarter wave plate and recombined with the same polarizing light splitter to form an output light having two orthogonal polarization elements. Measurement information of the desired distance or displacement is indicated by the phase difference of the orthogonal polarization elements of this output beam.

  This phase difference can be measured by various known methods. As an example, there is a method using a quadrature measuring device. Various quadrature measuring devices are known (for example, Patent Document 1).

JP-A-5-302809

The quadrature measurement apparatus generally includes a plurality of optical paths, a beam splitter, a wave plate, a polarizing plate, and a plurality of detection means. The phase difference of the quadrature signal, the amplitude error, the environmental sensitivity, the change with time, and the like are affected by the difference between the above-described elements and the arrangement of the plurality of optical paths. The errors associated with these differences are quite small and have often been overlooked or ignored in the past. However, the phase measurement result is affected by the quadrature phase error, and its accuracy may be limited. For this reason, in order to realize more accurate optical interference distance measurement, it is required to perform the above-described phase measurement with higher accuracy.
The main object of the present invention is to provide an apparatus for solving the above-mentioned problems.

As described above, when generating one or a plurality of measurement signals related only to the phase difference between the object beam output and the reference beam output, the polarization interferometer uses a phase difference detection unit (hereinafter also simply referred to as a detection unit). Often, the resolution and / or accuracy is limited by the influence of the function.
The present invention relates to a polarization interference phase difference detecting means having a novel configuration and improving the accuracy of phase difference measurement. In addition, since the phase difference measurement device has already become a mature technology, even if it is a small improvement, it has a significance in improving the accuracy and / or reliability of a widely used high-precision measurement technology. It is what you have.
Finally, phase difference measurements are used to provide higher measurement resolution and / or accuracy compared to the fundamental wavelength of radiation used in interferometers. Therefore, the usefulness of the measurement resolution of the detection means is sometimes called “interpolation level”. An interpolation level of about 1/100 of the wavelength is common. The detection means according to the invention provides an interpolation of about 1/1000 of the wavelength far beyond this level and / or increases reliability and reduces the effects of aging and environmental variables.

  In the present invention, the orthogonally polarized object of the output beam and the reference beam element are emitted toward a beam refracting element having polarization sensitivity, and the beam refracting element refracts one or both of these orthogonally polarized beams, A predetermined divergence angle is formed between these rays. The separated light is incident on the synthetic polarizing plate, and the light emitted from the synthetic polarizing plate is similarly polarized and interferes. Interfering separated rays then form interference fringes. The interference fringes may be parallel fringes. The spatial phase of the interference fringes of the detection means represents the phase between the object beam of the interferometer and the reference beam.

  In the present invention, the light refracting element having polarization sensitivity may be a prism having polarization sensitivity, such as a lotion prism, a Wollaston prism, or a Senalmon prism. Such a prism may stably refract one or both of the polarized light beams. In another aspect of the present invention, the prism having polarization sensitivity may be a monolithic element.

  In the present invention, the synthetic polarizing plate may be a rigid polarizing plate that is provided in the vicinity of the exit surface of a refractive element having polarization sensitivity and reduces or minimizes the intervening optical path. In another aspect of the present invention, the polarizing plate may abut on the exit surface of the refractive element having polarization sensitivity.

  In the present invention, the spatial phase of the interference fringes of the detection means is sensed by a light receiving element array that spatially filters the fringe pattern and generates a plurality of signals that are intentionally phase shifted by (360 / N) °. Also good. Here, N is an integer of 3 or more. In various embodiments, the light receiving element array may be periodic, and the center-to-center distance (pitch) of each light receiving element may be a fraction of the fringe spacing on the surface of the light receiving element array. In various embodiments, the stripe interval on the surface of the light receiving element array may be obtained by multiplying the pitch of the light receiving element array by an integer.

In the present invention, by adjusting the mounting angle of the light receiving element array, fringe spacing (stripe pitch) P _theta surface of the light receiving element array may be a predetermined relationship with the light-receiving element array pitch Pd. Specifically, the light receiving element array is a periodic light receiving element array in which the N light receiving elements are arranged so as to be slightly larger than M times the fringe pitch. The light receiving element array is disposed at a pitch Pd along the surface of the light receiving element array, and the surface on which the light receiving element is disposed is a surface substantially orthogonal to the optical path of the reference light beam element and the object light beam element. It is inclined by an angle α such that cos α = M * P _θ / N * Pd with respect to a reference plane whose normal is a straight line that bisects the angle θ.

  In the present invention, the light receiving element array may be provided in the vicinity of the exit surface of the polarizing plate to reduce or minimize the intervening optical path. In another aspect of the present invention, the light receiving element array may be attached to the surface of the polarizing plate.

  In the present invention, the light receiving element array spatially filters the fringe pattern to generate a three-phase output signal, and this three-phase output signal is subjected to signal processing when determining the spatial phase of the interference fringes to remove errors. You may do it.

  In the present invention, the light receiving element array spatially filters the fringe pattern to generate a quadrature output signal, and this quadrature output signal is signal-processed to determine the spatial phase of the interference fringes to remove errors. You may do it.

  In the present invention, a compact and monolithic detection means may be configured so that a light beam refracting element having polarization sensitivity, a synthetic polarizing plate, and a light receiving element array are provided together.

  In the present invention, only a single optical path that is an optical path of both the reference light beam and the object light beam that passes through the detection means and interferes with each other so that a light beam refracting element having polarization sensitivity, a synthetic polarizing plate, and a light receiving element array can be provided together In addition, all of the light receiving elements that generate the signal of the detection means may be arranged in the single optical path.

  In the present invention, the interference distance / interference displacement sensing device may be operated as follows. First, first and second light beams that are orthogonally polarized are emitted from a light source. The first light beam is incident along the reference optical path of the interferometer, and the second light beam is incident along the object optical path of the interferometer. The first light beam emitted from the reference optical path and the second light beam emitted from the object optical path are substantially parallel orthogonal polarizations, and are superimposed to form a combined output signal. The combined output light is incident on a light refracting element having polarization sensitivity, and the light refracting element includes first and second axes having polarization sensitivity. The first and second axes are arranged to be parallel to the polarization directions of the first and second light beams of the combined output light beam, respectively. The first and second light beams are emitted from a light refracting element having polarization sensitivity so that the divergence angle between them is a substantially predetermined nominal divergence angle and these light beams partially overlap. The first and second light beams that partially overlap pass through the polarizing plate. This polarizing plate has a polarization angle that substantially divides the angle between the polarizations of the first and second rays. An interference fringe pattern of substantially parallel fringes is formed by the polarization elements through which the first and second light beams have passed. The fringe pitch of the interference fringe pattern is constant, and the variable spatial phase is determined by the difference in the variable optical path length between the reference optical path and the object route. The spatial phase of the interference fringe pattern is detected using a light receiving element array. Here, the light receiving element array spatially filters the fringe pattern to generate a plurality of signals that are intentionally phase-shifted by (360 / N) ° (N is an integer of 3 or more).

  In the present invention, detection means used with a two-wavelength absolute interferometer may be provided. In this case, the phase is determined for each of the two distinct wavelengths that pass through the interferometer along the same optical path. In the first dual-wavelength embodiment, the beam splitter is placed after the light-refracting element with polarization sensitivity and provides two separate optical paths for the dual-wavelength detection means. A stripe pattern is formed by each of these two optical paths. Different wavelengths in each interference fringe pattern are separated using an optical filter for selecting wavelengths. The spatial phase of each fringe pattern is detected by each light receiving element array. Each of the light receiving element arrays is configured according to the above-described principle, and matches the fringe pattern of the wavelength that passes through each filter.

  In the present invention, the synthetic polarizing plate may be arranged before the non-polarizing light beam splitter along the optical path, and the two synthetic polarizing plates are arranged after the non-polarizing light beam splitter along the optical path and before the light receiving element array. You may arrange. In other embodiments that are useful in terms of simplicity and optical signal strength, a polarizing beam splitter may be used as a synthetic polarizer, in which case there is no need to provide another polarizer in the dual wavelength detection means. .

  In the present invention, a beam splitter is not essential even when dual wavelengths are used. In this case, the detection means is configured in the same manner as the single wavelength configuration described above. However, the diameter of the light beam and / or the size of the light receiving element is different in that it is configured such that two separate light receiving element arrays are arranged in a single interference pattern emitted from the synthetic polarizer. A filter for selecting a wavelength is arranged in front of each light receiving element array. Each light receiving element array is configured according to the principle described above, and matches the fringe pattern of the wavelength passing through each filter, and detects its spatial phase.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  In FIG. 1A, the interference distance measuring device 50 of this embodiment includes an interferometer unit 60 and a detection means 100.

The interferometer unit 60 generates a coherent light beam 65 using a laser source (not shown). The coherent beam 65 passes through the half-wave plate 70 and then enters the polarization beam splitter 75. The polarization beam splitter 75 passes a part of the coherent light beam 65, that is, P-polarized light, to form the reference light beam 86, and reflects a part of the coherent light beam 65, that is, the S-polarized light, to form the object light beam 76. . The reference beam 86 passes through the quarter wavelength plate 87, reaches the fixed reference mirror 88, and is reflected by the reference mirror 88 to the polarization beam splitter 75 through the quarter wavelength plate 87.
Here, the polarization direction is a state rotated by 90 ° from the polarization direction when first passing through the polarization beam splitter 75. In this way, the output reference beam 89 is reflected by the polarization beam splitter 75, and this output reference beam 89 is one of the orthogonal polarization elements of the combined beam 90 which is the combined interference measurement beam.

  Similarly, the object light beam 76 passes through the quarter wave plate 77, is reflected by the movable object surface 78, passes through the quarter wave plate 77, and is returned to the polarization beam splitter 75. Here, the polarization direction is a state rotated by 90 ° from the polarization direction when it is first reflected by the polarization beam splitter 75. In this way, an output object light beam 79 is obtained, and this output object light beam 79 becomes the other of the orthogonal polarization elements of the combined light beam 90.

The detection means 100 includes a light refraction element (PSBDE) 110 having a polarization sensitivity, a synthetic polarizing plate 130, and a light receiving element circuit 150.
As will be described in detail later, the combined light beam 90 having the incident cross-sectional dimension 113 is input to the PSBDE 110 that is oriented so as to divide the orthogonal polarization element of the combined light beam 90 by the divergence angle θ.
In the present embodiment, the PSBDE 110 is a lotion prism that passes the non-refracted light beam 120 and the refracted light beam 125 refracted at an angle 127. The PSBDE 110 may include a first crystal prism having a first axis and a second crystal prism having a second axis, and the first axis and the second axis may be orthogonal to each other. In this example, the divergence angle θ is the same as the refraction angle 127. Instead of PSBDE, a senalmon prism having the same function as PSBDE may be appropriately designed and oriented. In another example, the PSBDE may be a so-called birefringent type that refracts both rays at their respective refraction angles, and the divergence angle θ may be the sum of these two refraction angles. A birefringent PSBDE may consist of a Wollaston prism or a bi-dielectric grating with an appropriate structure, including the article “Wollaston prism-like devices based on blazed dielectric subwavelength gratings”. Wollaston prism device based on wavelength grating) ”(Haidar et al. Optics Express Vol. 13 No. 25 December 2005) can be used.

  The separated orthogonally polarized light beams then pass through a synthetic polarizing plate 130 that is oriented to have a polarization angle that is approximately half the polarization angle of orthogonally polarized light beams 120 and 125. Elements of the separated rays 120 and 125 that have passed through the synthetic polarizer 130 are similarly polarized, resulting in a substantially parallel fringe interference pattern. The spatial phase of the interference fringes of the detection means represents the phase difference between the object beam of the interferometer and the reference beam. The interference fringe pattern is formed on the light receiving element array 155 of the light receiving element circuit 150. The light receiving element array 155 can be a periodic light receiving element array having periodic receiving elements, for example, and the spatial phase of the interference fringes of the detecting means is determined by analyzing the signal generated by the light receiving element array 155. The Details will be described later. In general, if such a signal is generated, a light receiving element having a configuration that is currently known or will be developed in the future may be used.

  The interference fringe pattern may have a dimension 115 on the exit surface from PSBDE 110. This dimension represents the dimension of the region where the light rays 120 and 125 overlap. Note that this overlapping region becomes smaller as light propagates and separates, and the light receiving element array 155 has a size 117. It is advantageous to design the detection means so that the dimension 117 is larger than the dimension 157 of the light receiving element array 155. In this case, the entire light receiving element array 155 is covered with the interference fringe pattern, and the most suitable maximum signal can be generated. In various embodiments, the detection unit 100 may be downsized and designed and assembled, and the light receiving element array 155 may be provided in the vicinity of the synthetic polarizing plate 130 disposed in the vicinity of the exit surface of the PSBDE 110. These elements may be coupled together to form a stable and unitary assembly. Moreover, you may assemble these elements so that it may mutually contact | abut.

FIG. 1B is a diagram showing a detection means 100 ′ that is the same as or the same as the detection means 100 of FIG. 1A. It should be noted that the scales of the elements 135, 145, and 155 shown in the drawing are considerably emphasized for clarity of explanation.
FIG. 1B shows a wavefront set 135 of interference separation rays 120 and 125. Dashed lines 136a and 136b indicate parallel surfaces of the same intensity in the interference fringe pattern. These surfaces are surfaces extending inward and outward of the drawing sheet. The interference fringe intensity signal 145 schematically shows the intensity distribution of a sine wave or a near sine wave having a spatial period 140. The reference plane REF extends in the inner and outer directions of the page. The plane REF is orthogonal to the parallel plane 136a and the plane 136b, and is a normal line that divides the angle θ between the interference rays 120 and 125. As will be described later, the light receiving element array 155 forms a detection surface extending inward and outward of the paper surface and is disposed at an angle α with respect to the surface REF. When the intensities of the object beam 120 and the reference beam 125 are matched, the interference fringe pattern is generated with the following one amplitude.

Where λ is the wavelength of light, l _s is the optical path length of the object arm of the interferometer, l _R is the optical path length of the reference arm of the interferometer, and x is the parallel planes 136a and 136b (ie, Is a position along the direction orthogonal to the plane REF), x ₀ is the spatial offset, φ ₀ is the integrated phase difference offset of all optical elements along each optical path through the interferometer , Including the phase velocities of normal and extraordinary rays in the lotion polarizer.

The pitch of the interference fringe pattern, that is, the spatial period _Pθ has a relationship as expressed by the following formula with the divergence angle θ and the light wavelength λ.

The lotion quartz polarizer may be designed such that θ = 1.159 ° when the wavelength is 780 nm, so that the fringe pitch is P _θ = 38.6 microns. Furthermore, generally, when the divergence angle is selected from the range of 0.5 to 4.5 °, it is suitable for combinations with various light receiving element arrays that are practically used.

The light receiving element array 155 may be configured to generate N “spatial phase signals” (N is an integer greater than 0) corresponding to the M ^* stripe pitch. In general, when M is an integer larger than 0, the N light receiving element groups are distributed at regular intervals with _{respect to the} range M ^* P _θ (details will be described later, but may be slightly larger), and the above-described signal A set may be generated. The distance between the centers of the light receiving elements may be the light receiving element array pitch Pd. In various embodiments, as the light advances sequentially in the measurement direction, the N light receiving elements may generate N phase-shifted signals that are intentionally phase-shifted by an increase of (M ^* 360 / N) °. . The actual measurement, to allow for such tolerance and the divergence angle of the tolerances in the actual manufacture and assembly, N ^* Pd may produce a light-receiving element array 155 to be slightly larger than M ^* P _theta . In assembly or calibration, the light receiving element array 155 may be intentionally tilted by the angle α with respect to the surface REF so as to be expressed by the following expression.

FIG. 2 is an isometric view showing an example of a light receiving element circuit 250 having an example of the light receiving element array 255. The number of light receiving elements shown in the light receiving element array 255 is reduced to simplify the illustration. In general, providing a large number of light receiving elements is advantageous in that the signal intensity can be increased and errors can be averaged. For example, when Q is an integer of 3 or more, preferably an integer of 6 or more, it is desirable to provide Q ^* M ^* N light receiving elements.

An interference intensity profile 245 is shown. The pitch P ′ _θ is a fringe pitch seen on the detection surface 257 of the light receiving element array 255. In agreement with the description in FIG. 1B and Equation 3, P ′ _θ = (P _θ / cos α) and x ′ = (x / cos α). In this example, the light receiving element circuit 250 is set so that the fringe pitch is 1 (M = 1), the increase amount is M ^* 360 / N ° = 90 °, and the phase shift signal is 4 (N = 4). It's okay. Each light receiving element is configured with a light receiving element array pitch Pd. In this example, P ′ _θ = 4Pd, and each light receiving element is electrically connected (or connected in another manner) to a light receiving element at a position separated by 4Pd, and each of four light receiving element sets A (0 °), D (270 °), C (180 °), and B (90 °). Other examples of the configuration of the detection means will be described later.

  The fringe intensity profile 245 is disposed at an example of a position along the detection means measurement axis X ′. When the length of the object optical path changes by an arbitrary amount Δls, the phase difference between the interference rays 120 and 125 changes at 360 ° (2Δls / λ). Thus, the fringe intensity profile 245 follows the fringe and moves along the measurement axis X ′, with respect to any point on the fixed detector array 255, the spatial phase at 360 ° (2Δls / λ). Change. Each of the four light receiving element sets spatially filters the fringe intensity profile 245. Thus, each light receiving element set receives an optical signal, and this optical signal is a signal that periodically changes as a spatial phase change function of the interference fringe pattern on the detection surface 257.

A four-phase light receiving element circuit 250 shown in FIG. 2 is a known light receiving element circuit that generates a quadrature signal.
The light receiving element sets A to D receive optical signals that change sinusoidally according to the spatial phase of the fringe intensity profile 245. Each of the light receiving element sets A to D outputs an electrical signal proportional to the optical signal. That is, signal A (0 ° = “reference” phase) is to amplifier 226a, signal B (90 ° phase shift) is to amplifier 228a, signal C (180 ° phase shift) is to amplifier 226b, and signal D (270 ° relative) Phase shift) is transmitted to amplifier 228b. Signals A and C from amplifiers 226a and 226b are combined via differential amplifier 231, resulting in signal 1 (Sig. 1). Signals B and D from amplifiers 228a and 228b are combined via differential amplifier 232, resulting in signal 2 (Sig. 2). The differential signals (A-C) and (B-D) reduce or eliminate common mode “DC offset” errors that appear in the optical and electrical signals A-D. Signal 1 (Sig. 1) and signal 2 (Sig. 2) are substantially sinusoidal signals and are output with a phase of 90 ° (ie, signals 1 and 2 are quadrature signals).

FIG. 3 shows the general characteristics of the output signals 1 and 2 (Sig.1 and Sig.2), i.e. the displacement in the interferometer and / or the resulting change in the phase difference of the interfering rays 120 and 125 and / or The characteristics of the fringe intensity profile 245 as a function of the spatial phase change are shown.
Processing the quadrature signal in this way to determine the amount of displacement is a technique commonly used by those skilled in the art, and although it may not be necessary to elaborate here, the quadrature signal value Sig. . 1 and Sig. This will be briefly described with reference to FIG.

  Sig. 1 and Sig. Reference numeral 2 denotes a sine signal and a cosine signal. Therefore, the spatial phase of the fringe intensity profile 245 is represented by an arctangent function (Sig.1 / Sig.2) having an ambiguity of 180 °. This ambiguity may be removed by verifying the sign of the signal. Or Sig. 1 and Sig. 2 may be processed using an arctangent function of the second argument modulo 2π.

  The second argument “atan2” function of Equation 4 is used and described in many commonly available programs. The result of this function is Sig. / Sig. The inverse sine of 2 radians. However, by using the second argument, the quadrant of the angle can be determined and the result is between -pi and + pi, not between -pi / 2 and + pi / 2.

As described above, instead of using a four-phase detection means array, a three-phase detection means array may be used. In the case of a three-phase design, in one embodiment, the light receiving element circuit is a three-phase shift signal (N = 3) that is intentionally phase-shifted by an increase of (360 ° / N) = 120 °. You may comprise as follows. Each light receiving element may have P ′ _θ = 3Pd. Each of the light receiving elements is electrically connected (or connected by another method) to the light receiving element located at a position separated by P ′ _θ = 3 Pd, thereby outputting a three-phase signal representing the interference fringe pattern position or the spatial phase. Three light receiving element sets (A ′ (0 °), B ′ (120 °), and C ″ (240 °)) may be configured. An example of a method for connecting and processing a three-phase position signal is the three-phase position signal described in US Pat. No. 6,906,315, which is incorporated herein by reference in its entirety. The three-phase optical intensity signal can also be processed in the manner described in the aforementioned US patent, whereby two derived quadrature signal values may be determined. This signal is analyzed in the same manner as Sig to determine the fringe pattern position or spatial phase.

More generally, the practical number of phases of the phase signal (N phase signal) is determined by the light receiving element array and used in conjunction with suitable signal processing and analysis. Not all phase signals may be derived from a single section of the fringe intensity profile 245. For example, as an easy-to-understand example, the light receiving element circuit may be configured with a 4-phase shift signal (N = 4) at intervals of 3 ^* P′θ (M = 3), where P′θ is an angle α Nominal setting value associated with the nominal value. Thus, in this example, the light receiving element array pitch Pd = (3P′θ / 4) and the spatial continuous light receiving element are increased (M ^* 360 ° / N) = (3 ^* 360 ° / 4) = 270 °. Are intentionally phase shifted with respect to each other. This M / N ratio is representative among the ratio group used to remove the periodic error that occurs as the spatial second harmonic of the basic signal. The width of the light receiving elements in the array may be adjusted as necessary to maximize the signal and / or filter out other spatial harmonics. Each of the light receiving elements is electrically connected (or connected by other methods) to the light receiving elements located at a distance of 4 Pd, whereby four light receiving element sets (A ″ (0 °), D ″ (270 °)). ), C ″ (180 °) and B ″ (90 °)). In general, it is beneficial that the light receiving element array satisfies the condition of M ^* P′q = N ^* Pd (N> M) and that the Q ^* M ^* N light receiving element receives a fringe pattern. Here, M, N, and Q are integers. Which combination is most practical among (M = 1, N = 3), (M = 1, N = 4), (M = 2, N = 3) and (M = 3, N = 4) This depends on manufacturing constraints. In any combination, by analyzing multiple signals generated from light receiving elements at various phase positions in the interference fringe pattern, common mode errors in the optical signal are removed, and other errors are determined and corrected Can do. When all the light receiving elements used for detecting the phase signal are located in the single signal IC, an error caused by a difference between the respective light receiving element circuits can be removed as a common mode error.

  FIG. 4 is a flowchart illustrating an embodiment of the routine 400. The routine 400 is a series of operations for determining a value representing the phase difference between the coherent orthogonally polarized first and second rays of the combined ray using the detection means of the present invention. As shown in block 410, elements of orthogonal, linearly polarized, reference, and object rays that are superimposed on each other in the composite interferometric ray are provided. For example, such a combined beam may be output from a polarization interferometer having a configuration currently known or later developed. At block 420, a light polarizing element having polarization sensitivity is provided. The light beam polarizing element includes first and second axes that are orthogonal and have polarization sensitivity, at least one polarizing plate, and at least one light receiving element array. In block 430, the light polarizing element is oriented so that the first and second axes are parallel to the polarization of the reference light beam and the object light beam, respectively.

  At block 440, the reference and object ray elements of the combined ray are incident on a ray polarizing element having polarization sensitivity. In block 450, the reference beam element and the object beam element are output from the beam polarization element having polarization sensitivity at the divergence angle between the respective beam elements (predetermined divergence angle), and output. Elements are configured to partially overlap. At block 460, the partially overlapping reference and object ray elements pass through a polarizer having a pass axis that substantially divides the interpolarization angle of the reference and object ray elements. The light that has passed through the polarizing plate forms a substantially parallel interference fringe pattern. The fringe pitch of the interference fringe pattern is constant, and the variable spatial phase is determined by the phase difference between the reference ray element and the object ray element. At block 470, a spatial phase change of the interference fringe pattern is detected using a light receiving element that spatially filters the interference fringe pattern and outputs a plurality of signals that are phase-shifted relative to each other. Here, the relation including the plurality of signals represents a phase difference between the reference ray element and the object ray element of the synthesized interferometric ray.

  FIG. 5 shows a dual wavelength detector 500 as a first example of the dual wavelength detector. Such a detection means may be used with, for example, a two-wavelength absolute polarization interferometer. In that case, it is necessary to determine two phase differences for each of the two emission wavelengths λ and λ ′ passing through the interferometer along the same optical path.

  FIG. 5 is a schematic diagram of the detection unit 500. Elements labeled 590 and 690, 510, 520 and 620, 525 and 625, θ, 550 and 550 ′, 555 and 555 ′, REF and REF ′, α and α ′ are shown in FIGS. 1A and 1B. It may be designed, configured, and operated in a similar or identical configuration to elements labeled with reference symbols 90, 110, 120, 125, θ, 150, 155, REF, α. Each of the light beams 590, 520, and 525 is composed of light beam elements obtained by using the first radiation wavelength λ and similar to the light beams 90, 120, and 125 of FIGS. 1A and 1B. However, the rays 690, 620, 625 have a plurality of ray elements obtained using the second emission wavelength λ '. These are hereinafter referred to as a first wavelength element and a second wavelength element. Second wavelength elements 620 and 625 have the same polarization as first wavelength elements 520 and 525, respectively. As will be described in detail later, the second wavelength elements 620 and 625 are collinear with the first wavelength elements 520 and 525 until they are separated by filters 591 and 595 having wavelength sensitivity.

  As can be seen from the description in FIG. 1A, the structures of orthogonally polarized light beams 520 and 525 and orthogonally polarized light beams 620 and 625 are understood to be emitted from PSBDE 510. These rays enter a polarization beam splitter 575 having a polarization angle. Here, the polarizing beam splitter 575 can function as the synthetic polarizing plate 130 in FIG. 1A. The polarization angle of the splitter 575 is approximately half of the polarization angle between the orthogonally polarized light beams 520 and 525 and between the orthogonally polarized light beams 620 and 625.

The first wavelength elements 520 ′ and 525 ′ passing through the polarizing beam splitter 575 are polarized in the same manner as the second wavelength elements 620 ′ and 625 ′.
These interfere to form a first wavelength interference pattern and a second wavelength interference pattern that overlap each other. Since the second wavelength radiation is removed by the filter 591 having wavelength sensitivity, only the first wavelength fringe pattern reaches the light receiving element array 555. Here, in the light receiving element array 555, a first interference fringe pattern field is formed so as to cover the whole. The light receiving element array 555 is configured and arranged with an inclination, and outputs a signal to be analyzed in order to determine the spatial phase of the first wavelength interference fringes as described above. Thus, the phase difference between the first wavelength reference beam and the first wavelength object beam may be determined.

The first wavelength elements 520 "and 525" reflected by the polarizing beam splitter 575 are polarized in the same manner as the second wavelength elements 620 "and 625".
These interfere to form first and second wavelength interference patterns that are superimposed on each other. The filter 595 having wavelength sensitivity removes the first wavelength radiation, and only the second wavelength fringe pattern reaches the light receiving element 555 ′. Here, a second interference fringe pattern field is formed in the light receiving element array 555 ′ so as to cover the whole. The light receiving element array 555 ′ is configured and arranged with an inclination, and outputs a signal to be analyzed in order to determine the spatial phase of the second wavelength interference fringes. Thus, the phase difference between the second wavelength reference beam and the second wavelength object beam may be determined.

  As a modified example of the configuration of the detection means shown in FIG. 5, a non-polarizing light splitter may be used, and a synthetic polarizing plate may be disposed in front of the non-polarizing light splitter along the optical path. A polarizing plate may be disposed along the optical path at the rear stage of the non-polarizing light beam splitter and the front stage of the light receiving element array.

  FIG. 6 shows a dual wavelength detector 600 as a second example of the dual wavelength detector. FIG. 6 is a schematic diagram of the detection means 600. Elements denoted by reference numerals 590 and 690, 510, 520 and 620, 525 and 625, θ, 591 ′, 595 ′, REF and REF ′, α and α ′ are denoted by the same reference numerals in FIG. It may be the same as or the same.

  Based on the description of FIG. 5, the orthogonally polarized light beams 520 and 525 and the structure of the orthogonally polarized light beams 620 and 625 are understood to be emitted from the PSBDE 510. These light rays are incident on the synthetic polarizing plate 630 having a polarization angle. The polarization angle of the synthetic polarizing plate 630 is approximately half of the polarization angle between the orthogonally polarized light beams 520 and 525 and between the polarized light beams 620 and 625. The first wavelength elements 520 'and 525' passing through the polarizing beam splitter 575 are polarized in the same manner as the second wavelength elements 620 'and 625'. Therefore, they interfere to form a first wavelength interference pattern and a second wavelength interference pattern that overlap each other.

  Since the second wavelength radiation is removed by the filter 691 having wavelength sensitivity (schematically indicated by a broken line), only the first wavelength fringe pattern reaches the light receiving element 655. The light receiving element array 655 is configured and arranged with an inclination, and outputs a signal to be analyzed in order to determine the spatial phase of the first wavelength interference fringes as described above. Similarly, since the first wavelength radiation is removed by the filter 695 having wavelength sensitivity, only the second wavelength fringe pattern reaches the light receiving element 655 '. The light receiving element array 655 ′ is configured and arranged with an inclination, and outputs a signal to be analyzed to determine the spatial phase of the second wavelength interference. The dual wavelength detection means 600 may be designed so that the interference region 618 covers the entire light receiving element arrays 655 and 655 '. The design-related matters are as described above with reference to FIG. 1, and the same applies here. In order to satisfy this condition, the cross-section of the light beam and the optical element may be made larger if necessary.

  Lotion prisms have heretofore been used to separate a plane-polarized light beam of known orientation from other polarizing elements of the input light beam. That is, it can be said that it has been desired in the past to provide a considerably large divergence angle in order to completely separate a desired plane polarization output from other output rays at a short distance. Wollaston prisms have been used in the past to determine the polarization limit of input rays. The polarization limit is determined by comparing the intensity of the two output rays. That is, in order to completely separate one output light beam from another output light beam at a close distance, it can be said that it was conventionally desirable to provide a considerably large divergence angle.

  However, PSBDE in the detection means according to the present invention is used completely different from the conventional one. That is, the input beam is known to be orthogonally polarized, and the PSBDE axis is deliberately aligned with the orthogonal polarization direction to preserve the original orthogonal polarization, but nevertheless (depending on the type of PSBDE) Or both output rays can be refracted. If the divergence angle is very small, it may be inefficient or unusable in conventional applications, but it is desirable in the present invention.

  As shown in FIG. 6, as another embodiment, the PSBDE 510 may be a lotion prism. This lotion prism, suitable for this new and different application, has two non-coaxial crystal prisms 510a and 510b, which are formed from the same material and are in optical contact along an inclined surface 511. The optical axis of the crystal prism 510a and the optical axis of the crystal prism 510b are orthogonal to each other. In one embodiment, quartz is desirable as the non-coaxial crystal material because the values of normal and extraordinary refraction are fairly close. Therefore, if necessary, the divergence angle θ can be made smaller than 1 °.

As shown in FIG. 6, the light beam 590 from the interferometer is normal to the incident surface of the crystal prism 510a. The optical axis OA ₁ of the crystal prism 510a is also normal to the incident surface. The propagation direction of the light beam 590 is parallel to the optical axis OA _1, and both the P-polarized light and the S-polarized light have the same refractive index n _{0 in} the crystal prism 510 a. Optical axis OA2 of the crystal prism 510b is perpendicular to the optical axis OA _1, it is parallel to the surface 511. The “intersection angle” surface 511 forms an angle β with respect to the optical axis OA ₁ and is parallel to the optical axis OA ₂ . The incident angle I of the light beam 590 with respect to the surface 511 is I = π / 2−β. Since P-polarized light is oriented along the refractive index n ₀ in any crystal, it passes through the interface surface 511 without angular displacement. Thus, the normal ray incident angle is maintained so as to be normal to the incident surface and the exit surface of the polarizing plate, thereby forming the light ray 520.

S polarized light is oriented along the normal refractive index n ₀ in the first crystal, and is oriented along the extraordinary refractive index n _e in the second crystal. Therefore, the S-polarized light is refracted at an angle R obtained by the following formula 6.

  The divergence angle θ ′ between the S-polarized light and the P-polarized light at the prism 510b is as follows.

  The S-polarized light beam is refracted with respect to the exit surface of the second crystal. The angle divergence θ between the P-polarized light beam 520 and the S-polarized light beam 525 after being refracted on the exit side is as follows.

  Lotion prisms that provide divergence angles that are compatible with different detector array pitches may be set based on these relationships. In other PSBDE embodiments, other non-coaxial crystal prisms such as Wollaston prisms, Senalmon prisms, etc. may be designed and used based on similar principles.

  The preferred embodiments of the present invention have been described above. However, it will be readily understood by those skilled in the art that various modifications can be made in individual configurations and procedures. Therefore, various modifications can be made to the above-described embodiment as long as they do not depart from the object of the present invention, and these are also included in the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used as a phase difference detector and a phase difference detection method for measuring an interference distance that measures distance and displacement using optical interference.

It is a figure which shows one Embodiment of the interference distance measuring apparatus provided with the interferometer part and detection means of this invention. It is a figure which shows the detection means of the said embodiment of FIG. 1A typically, and shows the mode of operation | movement of this detection means. FIG. 3 is a partial isometric schematic view of an embodiment of a light receiving element array configuration that can be used in the detection means of the present invention and a light receiving element array circuit. It is a figure which shows the general characteristic of the output signal provided from the light receiving element array circuit of FIG. 2 according to the change of the detected interference fringe pattern. It is a flowchart which shows one Embodiment of a series of operation | movement routines for determining the value showing the phase difference between the coherent orthogonal polarization | polarized-light 1st light and 2nd light of a synthetic ray using the detection means of this invention. It is a figure which shows 1st Example of a dual wavelength detection means provided with the light beam refracting element which has a polarization sensitivity, and the light beam splitter for splitting the light beam inject | emitted from two separate light receiving element arrays. It is a figure which shows the other Example of the dual wavelength detection means of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Interference distance measuring apparatus 60 Interferometer part 79 Object light beam 89 which has object light beam element Reference beam 90 which has reference light beam element Synthetic light beam 100 as synthetic interference measurement light beam Detection means 110, 510 PSBDE as a light refracting element
127, θ Divergence angle 130, 630 as a predetermined divergence angle Synthetic polarizing plate 155, 255 as a polarizing plate Light receiving element array 500, 600 Dual wavelength detection means 520, 525 as detection means Light beam 520 ′ having a first wavelength element 525 ′, 520 ″, 525 ″ First wavelength element 555, 655 Light receiving element array 555 ′, 655 ′ as first light receiving element array Light receiving element array 575 as second light receiving element array Polarizing beam splitter 590 First light beam Rays 591, 691 as a set Filters 595, 695 as first filters Filters 620, 625 as second filters Rays 620 ′, 625 ′, 620 ″, 625 ″, second wavelength elements 690 having second wavelength elements Ray OA1 as the second ray set Optical axis OA2 as the first axis Optical axis Pd as the second axis Light receiving element pitch Pθ Stripe pitch Spatial period Sig of you. 1 Output signal 1 as first detection signal
Sig. 2 Output signal 2 as second detection signal

Claims (14)

A phase difference detection method for generating a signal indicating a phase difference between an orthogonal ray element, a linearly polarized ray element, a reference ray element, and an object ray element that are superimposed as a combined interference measurement ray to perform an interference distance measurement. ,
Installing a photorefractive element having polarization sensitivity with a first axis and a second axis orthogonal and having polarization sensitivity, at least one polarizing plate, and at least one light receiving element array;
The light refraction element having the polarization sensitivity is arranged so that the first axis and the second axis of the light refraction element are parallel to the respective polarizations of the reference light and the object light in the combined light. Process,
Inputting the reference beam element and the object beam element of the combined beam to the beam refraction element having the polarization sensitivity;
The reference beam element and the object beam element are output from the beam refracting element so that a divergence angle between these elements becomes a predetermined divergence angle θ, and the output reference beam element and the target are output. Partially overlapping the object ray element;
Passing the polarizing plate having a pass axis that substantially divides the angle between the polarization of each of the reference beam element and the object beam element through the reference beam element and the object beam element partially overlapping, The light passing through the polarizing plate forms an interference fringe pattern having substantially parallel stripes;
A step of spatially filtering the interference fringe pattern and detecting a change in the spatial phase of the interference fringe pattern using a light receiving element array that outputs N signals (N is an integer equal to or greater than 2) shifted in a fixed phase with each other And comprising
The interference fringe pattern has a constant fringe pitch P _θ determined by the wavelength λ of the reference ray element and the object ray element and the divergence angle θ, and between the reference ray element and the object ray element. A variable spatial phase determined by the phase difference of
A relationship including the value of the N signal indicates a phase difference between the reference ray element and the object ray element of the synthetic interferometry ray;
The step of detecting a change in the spatial phase of the interference fringe pattern includes a step of arranging a periodic light receiving element array so that the N light receiving elements are slightly larger than M times the fringe pitch. The light receiving elements are disposed along the surface of the light receiving element array at a light receiving element pitch Pd,
In the step of arranging the periodic light receiving element array, the N light receiving elements are substantially orthogonal to the optical paths of the reference light ray element and the object light ray element so that the N light receiving elements are slightly larger than M times the interference fringe pitch. A step of disposing the light receiving element on a surface to be processed, and the surface on which the light receiving element is disposed is cos α = M * with respect to a reference plane whose normal is a straight line dividing the divergence angle θ. A phase difference detection method characterized by being inclined by an angle α that satisfies P _θ / N * Pd. The phase difference detection method according to claim 1,
The step of arranging the light refracting element includes a step of providing any one of a lotion prism, a senalmon prism, a Wollaston prism, or a bi-dielectric grating. In the phase difference detection method according to claim 1 or 2,
The phase difference detection method, wherein the predetermined divergence angle is at least 0.5 ° and at most 4.5 °. In the phase difference detection method according to any one of claims 1 to 3,
M is an integer equal to or greater than 1, and combinations of M and N are (M = 1, N = 3), (M = 1, N = 4), (M = 2, N = 3) and (M = 3, N = 4). A phase difference detection method, wherein: The phase difference detection method according to claim 4,
The combination of M and N is M = 3 and N = 4. A phase difference detection method according to any one of claims 1 to 5,
A reference ray element and an object ray element, wherein the reference ray element and the object ray element to be superimposed in the combined interferometric ray include a reference ray element and an object ray element and have a first wavelength; and a reference ray element and an object ray element And a second ray element set having a second wavelength,
The first ray element set and the second ray element set have the same polarization direction and are substantially collinear;
The step of providing the at least one light receiving element array includes the step of providing a first light receiving element array and a second light receiving element array,
Providing a first filter that passes the first wavelength and blocks the second wavelength; and a second filter that passes the second wavelength and blocks the first wavelength;
A first wavelength interference fringe pattern having light of the first wavelength passing through both the first light ray element set and the second light ray element set along substantially the same optical path; and Forming a second wavelength interference fringe pattern having light;
By arranging the first filter having wavelength sensitivity in front of the first light receiving element array so that the first light receiving element array senses only the first wavelength interference fringe pattern, the first wavelength interference fringe pattern Detecting a spatial phase change of the first wavelength interference pattern, spatially filtering the first wavelength interference fringe pattern, and outputting at least two first detection signals that are fixed-phase shifted relative to each other;
The second wavelength interference fringe pattern is formed by disposing the second filter having wavelength sensitivity in front of the second light receiving element array so that the second light receiving element array senses only the second wavelength interference fringe pattern. Detecting a spatial phase change of the second wavelength interference fringe pattern, spatially filtering the second wavelength interference fringe pattern, and outputting at least two second detection signals that are fixed phase shifted relative to each other.
A relationship including a value of the first detection signal indicates a phase difference between the reference ray element having the first wavelength and the object ray element;
The relation including at least two values of the second detection signal indicates a phase difference between the reference light beam element having the second wavelength and the object light beam element. The phase difference detection method according to claim 6,
The step of providing the at least one polarizing plate includes the step of providing a polarizing beam splitter,
The step of passing the polarizing plate through the reference light beam element and the object light beam element that are partially overlapped with each other includes firstly passing light through the polarizing beam splitter and covering the entire first light receiving element array. Forming an interference fringe pattern field; and forming a second interference fringe pattern field to reflect the light to the polarization beam splitter so as to cover the entire second light receiving element array,
The first filter having wavelength sensitivity is disposed in front of the first light receiving element array in the first interference fringe pattern field;
The phase difference detection method, wherein the second filter having wavelength sensitivity is disposed in front of the second light receiving element array in the second interference fringe pattern field. A phase difference detector that generates a signal indicative of a phase difference between an orthogonal ray element, a linearly polarized ray element, a reference ray element, and an object ray element that are superimposed as a composite interferometric ray to perform an interference distance measurement. ,
A photorefractive element having a polarization sensitivity with a first axis and a second axis that are orthogonal and have polarization sensitivity;
A partially overlapping reference beam element and object beam are received from the beam refracting element, and a pass axis is disposed so as to substantially divide the angle between the polarization of the reference beam element and the object beam element. At least one polarizing plate,
Receiving at least one interference fringe pattern, spatially filtering the interference fringe pattern, and outputting N signals (N is an integer of 2 or more) that are fixed-phase shifted from each other, and at least one light receiving element array,
The light refracting element is disposed so that the first axis and the second axis are parallel to the reference light of the composite light and the polarization of the object light, respectively.
The light refracting element is configured such that the reference light beam and the object light beam received by the combined light beam are divergent angles between the light beam elements having a predetermined divergence angle θ, and the reference light beam element and the object light beam element partially Output so as to overlap
The light passing through the polarizing plate forms an interference fringe pattern of substantially parallel interference,
The interference fringe pattern has a constant fringe pitch _Pθ and a variable spatial phase determined by a phase difference between the reference ray element and the object ray element,
A relationship including the value of the N signal indicates a phase difference between the reference ray element and the object ray element of the synthetic interferometry ray;
The light receiving element array is a periodic light receiving element array arranged so that the N light receiving elements are slightly larger than M times the fringe pitch,
The light receiving elements are arranged along the surface of the light receiving element array at a light receiving element pitch Pd,
The surface on which the light receiving element is disposed is a surface that is substantially orthogonal to the optical path of the reference light beam element and the object light beam element, and is relative to a reference plane that is a normal line that bisects the divergence angle θ. , Cos α = M * P _θ / N * Pd is inclined by an angle α. The phase difference detector according to claim 8,
The light beam refracting element includes a lotion prism, a senalmon prism, a Wollaston prism, or a bi-dielectric grating. The phase difference detector according to claim 8 or 9,
The predetermined divergence angle is at least 0.5 ° and at most 4.5 °, the phase difference detector. The phase difference detector according to any one of claims 8 to 10,
M is an integer equal to or greater than 1, and combinations of M and N are (M = 1, N = 3), (M = 1, N = 4), (M = 2, N = 3) and (M = 3, N = 4). A phase difference detector. The phase difference detector according to claim 11,
The combination of M and N is M = 3 and N = 4. A phase difference detector according to any one of claims 8 to 12,
In the phase difference detector, wherein the light receiving element array includes a first light receiving element array and a second light receiving element array,
A first filter having wavelength sensitivity, disposed in front of the first light-receiving element array, which transmits a first wavelength of light and blocks a second wavelength of light;
A second filter having wavelength sensitivity, disposed in front of the second light receiving element array, blocking a first wavelength of light and allowing a second wavelength of light to pass through;
A first ray element set including the reference ray element and the object ray element and having the first wavelength, and a second ray element set including the reference ray element and the object ray element and having the second wavelength have the same polarization. The first light ray element set and the second light ray element set pass through the polarizing plate along substantially the same optical path and have the first wavelength when having a direction and being substantially on the same line. Forming a first wavelength interference fringe pattern having a second wavelength interference fringe pattern having light having the second wavelength,
The combination of the first filter and the first light receiving element array senses only the first wavelength interference fringe pattern, spatially filters the first wavelength interference fringe pattern, and is at least fixed phase shifted with respect to each other. Two first detection signals are output,
A relationship including a value of the first detection signal indicates a phase difference between the reference ray element having the first wavelength and the object ray element;
The combination of the second filter and the second light receiving element array senses only the second wavelength interference fringe pattern, spatially filters the second wavelength interference fringe pattern, and is at least fixed phase shifted with respect to each other. Outputs two second detection signals,
The phase difference detector, wherein the relation including the value of the second detection signal indicates a phase difference between the reference light element having the second wavelength and the object light element. The phase difference detector according to claim 13.
The polarizing plate receives a partially superimposed reference beam element and object beam element from the beam refracting element, and partially passes light to cover the entire first light receiving element array. A polarization beam splitter that forms an interference fringe pattern field and forms a second interference fringe pattern field so as to partially reflect light and cover the entire second light receiving element array;
The first filter is disposed in front of the first light receiving element array in the first interference fringe pattern field, and the second filter is disposed in front of the second light receiving element array in the second interference fringe pattern field. A phase difference detector.

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